Prepare your scantron: Use a pencil, not a pen! Fill in your name and fill the bubbles under your name. LAST NAME FIRST, First name second Put your 4-digit code instead of “IDENTIFICATION NUMBER”. --- (The last 4 digits of your OleMiss ID.) Question # 1: answer A Question # 2: answer D Question # 3: answer A Setup: Recall reading assignment: Chapter 15 (Stars): pp. 486 – 510 Please take a moment to mute your cell phone!

sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 4 What determines the length of life of a star? A All stars live the same length of time. B The temperature in its center. C Its chemical composition. D Its mass. E Its magnetic field. Next question coming …

sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21 Question 5 Which of the following uses the same physical process as the Sun to generate heat? A A gas stove. B A wood stove. C A hydrogen bomb. D An atomic bomb. E A nuclear reactor.

Nuclear processes Decay (occurs in nature) Fission (Reactors & A-bomb) Fusion (H-bomb) Nuclear processes Don’t confuse with chemical processes! They don’t change one atom into another.

Hydrogen to helium fusion This reaction needs heat > 1 million K (only in very center of star!) 4 H  He + heat (Call it H ‘burning’ - it is really not!) Mass of 1 proton 1.00867 units 4 protons 4.03468 units 1 He 4.00260 units Missing 0.03208 units = 0.8% Becomes energy: E = m c2

What if all hydrogen is gone? All stars start on the main sequence All stars become giants (when hydrogen is used up): This produces heat and keeps the red giant shining.

A-bomb does this Stars do this • More processes - helium fusion and beyond He + He + He  C + heat He + C  O + heat , ... • These processes need hotter and hotter temperatures Not in the Sun yet! • Energy is produced by fusion of heavier elements up to iron ”Metals” build up A-bomb does this Stars do this

Questions coming …

sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 6 What keeps a main-sequence star shining? A It burns hydrogen into water. B It produces helium from hydrogen. C It produces heavier elements from helium. D It is hot and cooling slowly as it gives off its heat. Next question coming …

sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 7 What keeps a red giant shining? A It burns hydrogen into water. B It produces helium from hydrogen. C It produces heavier elements from helium. D It is hot and cooling slowly as it gives off its heat. Next question coming …

sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 8 Which one comes first, the main sequence stage, or the red giant stage? A The main sequence stage. B The red giant stage. C It varies, depending on the chemical composition of the gas the star is born from. D It is not in order: heavy stars are born as red giants, light stars are born as main sequence stars. Next question coming …

sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21 Question 9 Which star lives longer, one with a small or a large mass? A The one with a large mass. B The one with a small mass. C All stars live the same length of time. D Not known: there is no-one who could observe newly formed or dying stars.

The life of a star: a losing fight against gravity Gravity pulls star together  contracts and is heated up  ignites Radiation pressure balances gravity: 4 H  He + heat * Small mass stars use hydrogen at slow pace - live a lot longer lifetime can be up to 100 billion years * The Sun is average: 10 billion years (halfway now) * Large mass stars use hydrogen at fast pace - live a lot shorter lifetime can be as short as 10 million years Inside a main-sequence star A losing fight 1

When all the hydrogen is gone What happens after all the hydrogen is gone? • Star collapses: inside heats up very hot • Helium “ignites”: heavier elements build up • Excess heat blows up the star large - becomes a red giant (cold outside) • On HRD - star moves off the main sequence When all the hydrogen is gone Why very hot inside? Needs extra high temperature to run against increased Coulomb barrier. Why small core? Needs to be small to increase gravity in order to maintain extra high temperature. Why bright? Needs extra power to hold up against increased gravity. Why large? Extra radiation pressure blows out atmosphere. Why cold atmosphere? Large size effectively cools outer layer. In the process the star blows off some of its stuff - explosions

More processes 3 4He 12C + heat 12C + 4He  16O + heat …. …  56Fe + heat These processes last shorter and shorter time (100 million yrs for the Sun) More processes At the end of that, no more heat  contraction again  center hot Either stops or blows up Not too heavy stars - strong enough to withstand gravity: WHITE DWARF Too heavy stars - not strong enough to withstand gravity: SUPERNOVA (Sun will stop at C and O mixture)

Questions coming …

sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 10 What keeps a normal (main sequence) star from collapsing under its own weight? A The strength of the rock it is made of. B The gravity of the star. C Radiation pressure due to the heat leaving the star. D The magnetic field of the star. Next question coming …

sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5 Question 11 In which of the two stages do stars spend more time of their life, as main sequence stars or as red giants? A About 100 times more time as red giants than as main sequence stars. B About 3 times more time as red giants than as C About equal. D About 3 times less time as red giants than as main sequence stars. E About 100 times less time as red giants than as